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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.read_at.overload5"></a><a class="link" href="overload5.html" title="read_at (5 of 8 overloads)">read_at (5 of 8 overloads)</a>
</h4></div></div></div>
<p>
          Attempt to read a certain amount of data at the specified offset before
          returning.
        </p>
<pre class="programlisting">template&lt;
    typename <a class="link" href="../SyncRandomAccessReadDevice.html" title="Buffer-oriented synchronous random-access read device requirements">SyncRandomAccessReadDevice</a>,
    typename Allocator&gt;
std::size_t read_at(
    SyncRandomAccessReadDevice &amp; d,
    uint64_t offset,
    basic_streambuf&lt; Allocator &gt; &amp; b);
</pre>
<p>
          This function is used to read a certain number of bytes of data from a
          random access device at the specified offset. The call will block until
          one of the following conditions is true:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
              An error occurred.
            </li></ul></div>
<p>
          This operation is implemented in terms of zero or more calls to the device's
          read_some_at function.
        </p>
<h6>
<a name="asio.reference.read_at.overload5.h0"></a>
          <span><a name="asio.reference.read_at.overload5.parameters"></a></span><a class="link" href="overload5.html#asio.reference.read_at.overload5.parameters">Parameters</a>
        </h6>
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<p class="title"><b></b></p>
<dl>
<dt><span class="term">d</span></dt>
<dd><p>
                The device from which the data is to be read. The type must support
                the SyncRandomAccessReadDevice concept.
              </p></dd>
<dt><span class="term">offset</span></dt>
<dd><p>
                The offset at which the data will be read.
              </p></dd>
<dt><span class="term">b</span></dt>
<dd><p>
                The <a class="link" href="../basic_streambuf.html" title="basic_streambuf"><code class="computeroutput">basic_streambuf</code></a>
                object into which the data will be read.
              </p></dd>
</dl>
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<h6>
<a name="asio.reference.read_at.overload5.h1"></a>
          <span><a name="asio.reference.read_at.overload5.return_value"></a></span><a class="link" href="overload5.html#asio.reference.read_at.overload5.return_value">Return
          Value</a>
        </h6>
<p>
          The number of bytes transferred.
        </p>
<h6>
<a name="asio.reference.read_at.overload5.h2"></a>
          <span><a name="asio.reference.read_at.overload5.exceptions"></a></span><a class="link" href="overload5.html#asio.reference.read_at.overload5.exceptions">Exceptions</a>
        </h6>
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<p class="title"><b></b></p>
<dl>
<dt><span class="term">asio::system_error</span></dt>
<dd><p>
                Thrown on failure.
              </p></dd>
</dl>
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<h6>
<a name="asio.reference.read_at.overload5.h3"></a>
          <span><a name="asio.reference.read_at.overload5.remarks"></a></span><a class="link" href="overload5.html#asio.reference.read_at.overload5.remarks">Remarks</a>
        </h6>
<p>
          This overload is equivalent to calling:
        </p>
<pre class="programlisting">asio::read_at(
    d, 42, b,
    asio::transfer_all());
</pre>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2018 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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